Effect of low dose Actinobacillus actinomycetemcomitans lipopolysaccharide pretreatment on cytokine production by human whole blood

Background and objective: Periodontal disease is known to influence the systemic condition in various ways, and the bacteria and their products, such as lipopolysaccharides (LPS), may spread from periodontal lesions via the systemic circulation to affect distant organs. The level of LPS in plasma from such patients is reported to be very low, and this low level of LPS is suspected to have priming or desensitizing effect. Thus, we investigated the effects of low dose LPS pretreatment on LPS-dependent cytokine production by whole blood cells ex vivo. Methods: Blood samples obtained from seven systemically and periodontally healthy individuals were pretreated with or without 5 pg/ml Actinobacillus actinomycetemcomitans LPS, followed by further stimulation with 1 ng/ml A. actinomycetemcomitans LPS. The concentrations of interleukin-1 beta (IL-1beta), IL-6, IL-10 and tumor necrosis factor-alpha (TNF-alpha) in the culture supernatants were then determined using enzyme-linked immunosorbent assay (ELISA). In addition, intracytoplasmic cytokine staining of whole blood cells was performed for flow cytometry. Results: Pretreatment with 5 pg/ml A. actinomycetemcomitans LPS significantly enhanced the production of IL- 1beta and IL-6 from whole blood when further induced by 1 ng/ml LPS (1.72 times higher for IL-1beta, 2.18 times higher for IL-6 than without pretreatment). The pretreatment did not enhance the production of either TNF-alpha or IL-10. Intracytoplasmic staining showed that the monocyte fraction was primarily involved in producing IL-1beta and IL-6. Flow cytometric analysis revealed that pretreatment increased the number of IL- 10 and IL-6 producing cells as well as mean fluorescence intensity of the stained cells. Conclusion: A low dose of bloodstream LPS found in periodontitis patients appears to be sufficient to prime monocytes, and may be capable of affecting the systemic responses of immune and inflammatory cells.